Conventionally, methionine, one of the α-amino acid compounds, has been used as a feed additive for animals. To produce the compound, acrolein is reacted with methyl mercaptan to produce 3-(methylthio)propionaldehyde, and this is further reacted with prussic acid, ammonia, and carbon dioxide to produce 5-(2-methyl-mercaptoethyl)-hydantoin (methionine hydantoin). Finally, this is hydrolyzed with an alkali to produce alkali metal methionate, and then neutralized by using an acid, for example, sulfuric acid or carbonic acid, to release methionine (see, for example, Patent Document 1, etc.).